Objectives: The clinical syndrome of spinal stenosis is a significant problem for older Americans. Although stenosis causes neurogenic claudication, spinal canal size does not accurately predict the severity of symptoms. A pilot study shows that paraspinal muscle denervation relates to spinal canal size in symptomatic persons. It is possible that paraspinal denervation is a more accurate marker for the clinical syndrome than anatomical imaging. Other research shows that paraspinal denervation in a particular distribution also occurs in younger asymptomatic persons, and denervation increases with age. It is possible that paraspinal denervation causes subtle hypermobility and contributes to Kirkaldy-Willis's degenerative cascade of facet hypertrophy and canal stenosis. Specific Aims: 1. To assess whether paraspinal EMG scores or MRI measurements of stenosis relate best with the clinical syndrome in older persons. 2. To assess whether paraspinal EMG scores predict future symptoms of stenosis and future symptom severity in older persons with and without spinal stenosis. 3. To assess whether change in clinical status relates better to change in paraspinal EMG scores or change in MRI measurement of stenosis. 4. To assess the rate of denervation of the paraspinal muscles in older persons with and without back symptoms. Research Design: Blinded longitudinal study. Methods: Five groups of 30 subjects older than 55 years old, including: asymptomatic persons (healthy persons without low back pain) from the community, persons with lock back pain (LBP) but no stenosis on MRI, persons with stenosis symptoms with mild, moderate, and severe radiographic findings. An experienced neuroradiologist will measure spinal canal size and assign subjects to appropriate categories. A patient questionnaire, physical examination, a walking tolerance test with long latency nerve conduction studies (F- and H- waves) before and after walking, a 7-day pedometer test, and a measure of the flexion-relaxation phenomenon will be administered to the subjects. An unblinded examiner will perform one aspect of the MiniPM paraspinal EMG technique to acclimatize the patient, then a blinded examiner will perform the entire MiniPM, one extremity EMG, sensory and motor nerve conduction studies. Subjects will repeat the test battery (MRI, EMG, and clinical evaluation) approximately 18 months later. Appropriate statistics will test each of the four hypotheses.